Ask HN: What's the best resource for getting back up to speed with modern css

I used to know my way round front end design techniques a couple of years ago, but I guess I'm no longer current. I'd like to know what people regard as the best resources available at the moment for the front end stuff that's changed:

* CSS transitions * CSS3 * SASS/other compilers * Styling in JS.

Basically, what are the cool kids doing nowadays?